One thing I often hear regarding evolution is the notion that it can end. That is, I hear people make the claim that in one way or another, a species can (or has) reached a point where it will no longer evolve. This idea is generally applied exclusively to humans, but perhaps advocates would extend their arguments. I’m not sure. At any rate, it’s a surprisingly popular claim. Geneticist Steve Jones even made a version of it. He was speaking more of rates than anything, and I’m likely to chalk up his statements to hyperbole, but he did title one of his talks, “Human Evolution is Over.” Unfortunately for him, he’s wrong.
Evolution at its most basic is the transmission of genes from one organism to another. That isn’t to say individuals can evolve – they can’t – but broken down to its constituent parts, evolution is the flow of alleles from one vehicle (individual organism) to another. So long as that is occurring, evolution is occurring. To put it another way:
Evolution happens every single time an organism reproduces.
Evolutionary rates – generation time, mutational rate, environmental pressures, frequency of drift, etc – will vary from species to species and over great swaths of time, but they can never reach zero for any given population unless that population ceases to exist. At the point where members of the group no longer produce offspring is when evolution stops. It is literally the only time it can stop.
The fact is, evolutionary theory is the most integral part of the field of biology. The famous Theodosius Dobzhansky paper and now phrase, ‘Nothing in biology makes sense except in the light of evolution’, couldn’t be any more true; from the moment the first replicator evolved into something more, evolution has not once taken a break. So long as there is life, there is evolution.